This invention relates to a cell image processing system having a bus dedicated to image data. More particularly, the invention relates to a method and apparatus for processing cell images in which, even if a number of cells are captured in a single imaged frame, various cell image parameters regarding a number of cells, such as cumulative chromaticity information, chromaticity histograms, cumulative gradient information and gradient histograms, can be efficiently obtained in one frame cycle from edge detection information relating to the cells.
The general architecture of an image processing apparatus having a bus dedicated to image data, as well as the operation of this apparatus, will now be described in simple terms.
FIG. 1 is a block diagram illustrating an example of an image processing apparatus having a bus dedicated to image data.
The apparatus includes a general-purpose microcomputer 12 which functions as the overall host processor of the system, a plurality of slave boards for processing an image in hardware fashion, and a master controller and processor 14 for controlling the operation and function of the slave boards. More specifically, each board is operated by having its operating mode, function and parameters set by the master controller and processor 14 via a slave board control bus 16. The boards usually are interconnected via a six-to-nine channel bus 18 decicated to image data, with an eight-bit bus serving as one channel.
The data on the dedicated bus flow in the manner of a time series identical with that of a raster scan system in television, and one-sixtieth of a second is required to deliver all of the data in a single image frame. In other words, the bus dedicated to the image data employs horizontal and vertical synchronization as the timing base, and random accessing for a single image frame of data cannot be performed via the data bus 18. Because the dedicated bus uses vertical synchronization as a timing base, the processing performed by the boards connected thereto also has the vertical synchronization cycle (one-sixtieth of a second) as a single processing cycle. Accordingly, the setting of the operating mode, function and parameters of the slave boards by the master controller and processor ordinarily is carried out during the vertical blanking period. The master controller and processor not only controls the slave boards in accordance with an image processing request from the general-purpose microcomputer but also functions to compute such characterizing parameters as the cell edge trace, cell image area and perimeter of the cell images based on data obtained through processing performed by an image processor board 20. Furthermore, it is also possible for the master controller and processor to randomly access the contents of image memory boards 22, 24 via the slave board control bus, ascertain the position at which a cell appears, read the image data pertaining solely to this portion and compute other characterizing parameters.
The general operation of the common image processing apparatus set forth above will now be described taking as an example a case in which a still picture of cells flowing in a planar sheath is captured and the cells are classified in accordance with type by means of image processing.
A planar sheath flow refers to a flow having a thickness the same as that of the thickest particle among the particles of interest and a width a number of times greater than that of the widest particle, e.g., a width which can be 100 times greater or more, wherein the flow is such that the particles of interest in the flow will not overlap one another in the direction of thickness. Examples of an apparatus in which a planar sheath flow is realized are disclosed in the specifications of Japanese Patent Publication No. 57-500995 and U.S. Pat. No. 4,338,024.
In order to acquire a still picture of cells in a planar sheath flow, strobe light or pulsed laser light having a short emission time is made to irradiate the flow from the thickness direction thereof, and an image is formed on the image pickup surface of a video camera (color camera) via an objective lens. The camera outputs analog signals resolved into the three colors R (red), G (green) and B (blue). These are fed into an image input board 28 which subjects them to an analog/digital (A/D) conversion. The resulting digital R, G and B data is stored in an image memory board 22 via a three-channel image data bus. At the same time, the data is inputted also to the image processor board 20, which executes preprocessing for determining whether a cell is in view and for detecting the edge of the cell. Preprocessing entails extracting an average value of, e.g., G (green) and B (blue) data at each point (pixel) of an image and forming a histogram of the entire image frame in realtime. The data processed by the image processor board 20 is stored in the image memory board 24 via the dedicated bus 18. Though the method in which the two image memory boards 22, 24 are used is not particularly limited, in the present description the image memory board 22 shall be used to store original image data and the image memory board 24 shall be employed to store data which has been processed.
In one vertical blanking period the master controller and processor 14 checks the histogram prepared in the image processor board 20 and determines whether a cell is present in a single imaged frame. If it is decided that no cell is present, then the program of the master controller and processor 14 returns to processing for the next imaged frame. When a cell is found to exist, the program proceeds to the next image processing step. An example of the next image processing step would by processing for subtracting previously stored background data from the imaged data, preparing a histogram from the results obtained, binarizing the image data as preprocessing for the purpose of tracing the edge of a cell, and detecting the cell edge. The resulting edge detection data is stored in the image memory board via the bus dedicated to image data. By way of example, edge detection information might include eight-bit data made to correspond to each pixel of a single image frame, in which pixels that take on value other than 0 are regarded as cell edge points and the direction in which the next neighboring cell edge point is located is indicated by the particular value. When this processing is completed, the master controller and processor 14 refers to the edge detection information in the image memory board via the slave board control bus 16, and the edge of each and every cell is traced by means of a microprogram. At the same time, computations for the area and perimeter of each cell, cumulative chromaticity information and shape parameters are performed. Each cell is then classified based on the characterizing parameters obtained.
In a system in which it is required to save (store) images of the cells observed, processing is necessary in which the position occupied by each cell in the frame is determined from the results of edge tracing for each cell, partial regions of the original frame in which cells are present are extracted, and the regions are gathered together in accordance with each cell class and saved in memory. The cell image data saved in accordance with each class is inputted to a display processor board 30 via the dedicated bus 18 and is displayed on a color monitor 32. This completes the brief description of image processing performed by an image processing apparatus having a bus dedicated to image data.
A problem which the present invention attempts to solve concerns processing for obtaining, in a highly efficient manner, cell image parameters which are valuable characterizing parameters of each cell image, namely cumulative chromaticity information, chromaticity histograms and cumulative gradient information, which represents the complexity of cell interior, for each of the three colors R, G and B.
Let the image data indicative of cell interior be represented by R(i,j), G(i,j) and B(i,j) for these three colors. Cumulative chromaticity information in each of these colors within a cell will then be expressed by EQU .SIGMA. R(i,j), .SIGMA. G(i,j), .SIGMA. B(i,j)
respectively.
As shown in FIG. 9, a chromaticity histogram is a graph in which the chromaticity of each pixel of a cell interior is plotted along the horizontal axis and the number of pixels (frequency) having this chromaticity value is plotted along the vertical axis.
Cumulative chromaticity information and the chromaticity histogram can be extremely important in cases where cells are capable of being dyed in different colors using certain suitable dyeing solutions in order to identify and classify the cells.
A conventional method of obtaining the aforementioned cell image parameters in an image processing apparatus having a bus dedicated to image data will now be described.